1. Field of the Invention
This invention relates to the production of polyurethane materials from polyols based on randomized castor oil and isocyanates. The mechanical properties of the polyurethane materials according to the invention are comparable with those of the materials obtainable from unmodified castor oil, although the gel time of the systems is far longer.
2. Discussion of Related Art
The use of castor oil and/or other hydroxyfunctional triglycerides for the production of polyurethanes has been known for some time. For example, the production of elastomers from castor oil and corresponding isocyanates is described in Saunders, Frisch: "Polyurethanes: Chemistry and Technology, II Technology", Interscience (1964). However, optimal processing of these generally two-component systems involves a long gel time, i.e. the time during which the mixture of the two components can undergo irreversible changes in its external form should be considerable. A long gel time is of advantage above all where two-component (2C) systems are used for the production of coatings because, on the one hand, better flow is guaranteed and, on the other hand, the degassing time available to the system is clearly increased which can contribute towards reducing bubble formation. Overly short gel times can lead to poor processability of the polyurethane systems, for example even in summer or in countries with a generally fairly high ambient temperature.
Whereas the use of catalysts, such as dibutyl tin dilaurate for example, has generally been regarded among experts as the easiest solution to the problem of shortening the gel time, increasing the gel time is far more difficult. An extended gel time was achieved, for example, by incorporation of low molecular weight polyols although this resulted in a possibly unwanted deviation from the originally planned material properties. Accordingly, attempts to extend the short gel time or pot life of the mixtures without affecting material quality have hitherto failed.
Accordingly, the problem addressed by the present invention was to modify oleochemical polyols based on castor oil in such a way that, on the one hand, the polyol component could be processed to materials, such as casting resins or two-component foams for example, having the required mechanical properties while, on the other hand, the gel time of the polyols could be extended as required for their use in two-component systems.
It has now surprisingly been found that randomized castor oil, which is obtainable by heating castor oil at temperatures above 100.degree. C. in the presence of lithium as catalyst, leads to a significant increase in the gel time without adversely affecting the properties of the polyurethane resin.